It is known that microwave ovens may have “hot spots”, that is, areas in which the microwaves are concentrated and may become amplified, thereby causing a food item in the hot spot to become intensely heated. A single operating mode microwave oven may have only one hot spot in a single, constant location in the microwave oven, while a multiple operating mode microwave oven may have multiple hot spots in various places in the microwave oven at different points in time, thereby reducing the effect of each individual hot spot over the duration of the heating cycle. In many instances, the microwave oven may be provided with a turntable to attempt to mitigate the effect of such hot spots by continuously rotating the food item (and container, where applicable) to distribute the effect of the hot spots over various portions of the food item. However, in other instances, the microwave oven may be designed to utilize such hot spots advantageously with no attempt to mitigate the effect of the hot spot, for example, by specifying to the user which areas of the microwave oven will heat a food item most rapidly (e.g., a beverage).
It also is known that some microwave heating containers that include one or more microwave energy interactive elements may inherently have “hot spots”, that is, areas that are more prone to overheating under certain microwave heating conditions. For example, some microwave heating containers include a microwave energy shielding element to prevent the overheating of particularly vulnerable areas of food item, such as the sides and peripheral margin of the bottom of the food item. Depending on the shape of the shielding element, the food item being heated, the length of the heating cycle, the type of microwave oven, and so on, some areas of the container adjacent to the shielding element may be more prone to scorching than other areas of the container.
The combined effect of the hot spots in the microwave oven and the hot spots in the container may cause substantial overheating and/or charring of the construct. By way of example, FIG. 1A depicts a top plan view of an exemplary microwave heating construct (e.g., a tray) 100 formed at least partially from a generally disposable material, for example, paper, paperboard, and/or polymeric materials.
The tray 100 includes a substantially oval base 102, a substantially upstanding wall 104 extending upwardly from the base 102, and a cavity 106 for receiving a food item generally defined by the base 102 and wall 104. The uppermost portion of the wall 104 comprises a rim 108. A microwave energy shielding element 110 overlies a portion of the base 102 and extends upwardly along the wall 104 a substantially uniform distance (e.g., height H) from the base 102, as shown schematically by stippling in FIG. 1B. In this and other embodiments, the microwave energy shielding element 110 generally comprises a metallic foil or high optical density material operative for reflecting substantially all of impinging microwave energy. The shielding element 110 circumscribes (i.e., surrounds) a plurality of elongate, somewhat reniform (i.e., kidney bean shaped) microwave energy transparent areas 112 and substantially obround microwave energy transparent areas 114 respectively disposed along the corners 116 and sides 118 of the tray 100. The microwave energy transparent areas 112, 114 comprise apertures in the microwave energy shielding element 110.
The present inventors have determined that when the tray 100 is heated under no load conditions (i.e., without a food item) in a microwave oven, the tray 100 may tend to overheat and char in the corners 116 of the tray 100 in the areas A adjacent to the shielding element 110. Even more significant charring may occur when the tray 100 is heated under no load conditions in a microwave oven having a single mode with one of the corners 116 positioned in the hot spot of the microwave oven and/or when the tray 100 is heated in a microwave oven without a turntable. Such charring also may occur when a food item is contained in the tray, which may cause overheating and/or overdrying of the adjacent portions of the food item.
Accordingly, there is a need for a method of reducing hot spots in a microwave heating container. There is also a need for a microwave heating container that mitigates the adverse effects of hot spots in a microwave oven. There also is further a need for a container that is capable of being heated in a single operating mode microwave oven and/or a microwave oven without a turntable without being prone to substantial charring.
Other features, aspects, and embodiments of the invention will be apparent from the following description, accompanying figures, and appended claims.